1. Field of the Invention
This invention relates to catheters generally and more particularly to steering mechanisms that promote the transit of such catheters through the blood vessels of a patient.
2. Description of Related Art
Steerable mechanisms have been developed to facilitate the transit of catheters through a patient's blood vessels. In practice, a surgeon typically observes the catheter fluoroscopically and maneuvers the catheter by selective rotation and deflection of a steering mechanism of the proximal end of the catheter. The rotation and deflection at the proximal end bends or deflects the tip of the catheter and enables the surgeon to steer the catheter as it advances through the tortious path often found during the transit through a patient's blood vessels.
In many applications the ability to steer the catheter is crucial to the success of the therapeutic protocol and can be a factor in reducing risk to and trauma of the patient. Moreover, the ability to steer the catheter impacts the speed and ease by which the surgeon can properly position the distal end, particularly during heart mapping protocols.
The distal ends of some steerable catheters are formed of a shape memory material or structure, such as a coil spring, so that the application of a force to a steering mechanism in the form of a steering cable deflects the distal tip from its normal position. Then as the tension in the cable is released, the distal end tends to return to its normal position. Other prior art steering mechanisms are often carried within the catheter or as part of the wall structure of the catheter to improve the response of the distal end tip to a steering force applied at the proximal end. Such steering mechanisms are designed to simplify the surgeon's task of orienting the distal end tip for deflection in a proper direction, and following United States Letters Patents and United States Patent Application describe various steering mechanisms for use with catheters:
______________________________________ 4,798,598 (1989) Bonello et al. 5,037,391 (1991) Hammerslag et al. 5,108,368 (1992) Hammerslag et al. 5,190,050 (1993) Nitzsche 5,228,411 (1993) Lundquist 5,242,441 (1993) Avitall 5,322,064 (1994) Lundquist Serial No. 08/138,863 (1993) Mirarchi et al. ______________________________________
Bonello et al. disclose a catheter having a distal end with an overcoated coil spring formed with closely spaced coils at distal and proximal end portions thereof and with relatively widely spaced coils at a central portion. A traction member connects to one side of the coils in the distal end portion and extends distally through the catheter and a proximal handle. Retraction of the traction member by a control device in the handle urges the coil spring to bend about its central portion. Upon releasing the traction member from its retracted condition, the coil spring tends to urge the distal end of the catheter to resume its normal condition.
Each of the Hammerslag et al. patents disclose a steering mechanism for use in a steerable guidewire or catheter. The steering apparatus includes a flexible post disposed in the guidewire or catheter near a flexible distal end thereof. A plurality of circumferentially spaced steering wires connects to the flexible post intermediate its distal end and its fixed proximal base and extends through the guidewire or catheter to a handle. Retracting certain steering wires relative to the others deflects the steering post and consequently urges a similar deflection of the flexible distal end of the catheter or guidewire. Another embodiment discloses a flexible steering ribbon having an intermediate hinged portion positioned in a flexible distal end of a guidewire or catheter. Two steering wires extend from a handle of the guidewire or catheter along opposed sides of the ribbon and secure to a distal end of the ribbon. Retraction of one wire relative to the other causes the ribbon to bend at the hinge and deflects the distal end of the guidewire or catheter.
Nitzsche discloses a steering mechanism comprising three elongated, thin flat shims sandwiched together at a distal end of the shims and disposed at the distal tip of the catheter. A structure within the catheter tube supports and fixes the proximal position of the center shim. A first cable connects the proximal end of one of the other two shims with a handle; a second cable elastically connects the third shim to the handle. Proximal displacement of a slide portion stretches the elastic cable while sliding the shim connected to the other cable proximally to deflect thereby the distal end of the sandwich. When the slide is released, the elastic anchor contracts and returns the sandwich to its original orientation.
Each Lundquist reference discloses a catheter that includes an elongated tube and proximal handle. Steering wires and a torque tube extend from the handle distally through the tube with distal ends of the steering wires secured to spring elements extending from the distal end of the torque tube. A proximal end of each of the steering wires secures to opposed portions of a rotatable eccentric secured in the handle. The torque tube rotates the distal end responsive to rotation of the handle, while rotation of the eccentric urges deflection of the distal end. Specifically, rotation of the eccentric in a first direction tensions one of the steering wires and reduces the tension of the other steering wire. The resulting differential tensioning of the steering wires deflects the end selectively toward the steering wire under the greater tension. Another embodiment disclosed by Lundquist in U.S. Pat. No. 5,322,064 includes first and second rotatable collars on a handle that attach to the first and second steering wires, respectively, so that selective rotation of the collars varies the relative tension of the associated steering wire to enable radial deflection an X-Y plane and, by rotation of the handle, in a transverse Z plane.
In Avitall a steering wire extends through a catheter between a sliding portion of a handle at the proximal end of the catheter and a flexible portion at a rotatable distal tip. Retracting the slide handle deflects the distal tip from its normal linearly extending axial orientation.
U.S. patent application Ser. No. 08/138,863 to Mirarchi et al. discloses a steerable catheter including a steering wire that extends between and connects a distal end tip with a handle at the proximal end. A proximal portion of the handle attaches to the catheter tube. Sliding a base portion of the handle relative to the proximal portion in first and second directions respectively increases and decreases the tension on the cable to enable deflection and return to an undeflected condition. In an alternative embodiment, an intermediate portion of the cable extends along a looped path defined in the base of the handle so that the handle functions as a movable pulley. Consequently a given axial displacement of the handle produces twice that displacement of the cable at the distal end.
Although the foregoing prior art references describe catheters with steering mechanisms for deflecting the distal tip, they all are characterized by restrictions that limit their convenient use. For example, the steering mechanisms disclosed by Mirarchi et al., Nitzsche and Bonello can only be deflected in a single direction and require the surgeon to rotate the handle up to 180.degree. to orient the distal end properly for deflection in a desired direction. Since repeated reorientations of the catheter tip frequently are required, the therapeutic protocol of these devices necessitates extra work, skill and effort on the part of a surgeon and prolongs the procedure. Each of the Lundquist references provides for bidirectional bending of the distal end thereby limiting the angular displacement to 90.degree.. However, the rotary displacement of the eccentrics or separate collars can be inconvenient to surgeons accustomed to linear actuators and may even require the surgeon to use both hands. Additionally, at least one embodiment disclosed by Lundquist requires separate controls that may lead to mistakes in steering.
The pulley arrangement disclosed by Mirarchi et al. provides the user with a slide apparatus that has a greater than unity mechanical advantage over the devices disclose by others of the references. That is, for a relatively short displacement of the slide handle relative to the catheter, the steering wire is displaced at a multiplied rate. This provides for greater ease of use of the device. Nevertheless, the apparatus disclosed by Mirarchi et al. has the previously discussed limitation of single direction deflection.
Thus, steering mechanisms of the prior art fail to provide a handle with a slide mechanism for selectively deflecting the distal end of the catheter tube in two directions relative to an axial orientation. These steering mechanisms also fail to disclose a bidirectional steerable deflectable catheter in which the steering mechanism also provides a greater than unity displacement of the distal end tip for a given displacement of a slide mechanism in at least one of the two deflectable directions.